The present invention relates to a process for preparing a butanetriol derivative, which is important as an intermediate in making antidiabetics having protein kinase C inhibiting activity and relates to a novel intermediate of the butanetriol derivative.
Butanetriol derivatives are used as intermediates in making antidiabetics having protein kinase C inhibiting activity. It is known that butanetriol derivatives are prepared by reacting glycidyl trityl ether and vinylmagnesium bromide, by allyl-etherification and by ozonolysis of resulting olefin, followed by treatment of resulting aldehyde with sodium borohydride (U.S. Pat. No. 5,541,347).
Glycidyl trityl ether, however is expensive and the reactions with vinylmagnesium bromide and by ozonolysis have to be carried out at lower temperature, xe2x88x9220xc2x0 C. and xe2x88x9235 to xe2x88x9250xc2x0 C., respectively. The procedures, therefore are troublesome. Furthermore, ozone is harmful to human body and there is a possibility of explosion. Thus, the known methods are not satisfactory for application to industrially scaled production. The superior method has been desired.
As a result of extensive investigation on an improved method for preparing butanetriol derivatives, the present inventors have found that butanetriol derivatives can be favorably prepared in industrial scale by using the starting material which is easily available.
The present invention relates to a novel process for preparing a butanetriol derivative, which is important as an intermediate in making antidiabetics having protein kinase C inhibiting activity and relates to a novel intermediate thereof.
The process for preparing a butanetriol derivative (1) of the present invention is shown as the following reaction scheme. 
In the above formulae, R1 and R2 are, different from each other, protecting groups for alcohol and said protecting groups are such that only R2 is removed when deprotection reaction is carried out. R3 and R4 are, the same or different, hydrogen, C1-C4 alkyl or phenyl, or may form a C3-C6 cycloalkyl group together with the adjacent carbon atom. X is halogen atom or sulfonyloxy group.
Each step is explained below in detail.
Compound (6) is prepared from compound (7).
Introduction of the protecting group (R2) except tetrahydropyranyl group is carried out by etherifying hydroxy group for compound (7) in the presence of a base to give compound (6).
Examples of the protecting group are silyl ether-protecting groups, such as triethylsilyl, tert-butyldimethylsilyl or tert-butyldiphenylsilyl, benzyl-protecting groups, such as benzyl, p-methoxybenzyl or trityl, and acetal-protecting groups such as methoxymethyl etc.
Introduction of tetrahydropyranyl group is carried out by reacting compound (7) and dihydropyrane in the presence of acid catalyst, such as p-toluenesulfonic acid or pyridinium p-toluenesulfonate.
Preferable protecting groups are tert-butyldimethyl-silyl, tert-butyldiphenylsilyl, benzyl and p-methoxybenzyl, especially tert-butyldimethylsilyl and benzyl.
Introduction of the protecting group except tetrahydropyranyl group is carried out by reacting hydroxy group of compound (7) with an alkylating agent in the presence of a base.
Examples of the base used in this reaction are alkali metal or alkaline earth metal hydroxides, such as sodium hydroxide or potassium hydroxide, alkali metal or alkaline earth metal hydrogen carbonates, such as sodium hydrogen carbonate or potassium hydrogen carbonate, alkali metal or alkaline earth metal carbonates, such as sodium carbonate or potassium carbonate, alkali metal or alkaline earth metal hydrides, such as sodium hydride or potassium hydride, organic alkali metal salts, such as dimethyl sodium, n-butyllithium, sec-butyllithium or tert-butyllithium, and alkali metal amides, such as lithium diisopropylamide, potassium diisopropylamide, sodium hexamethyldisilazide, potassium hexamethyldisilazide or lithium hexamethyl-disilazide.
Amount of the base is equimole or more than equimole to the substrate, preferably 1.0 to 1.2 moles. Regarding of silyl ether-protecting groups or benzyl-protecting groups, examples of the reacting agent used for protection are silyl halides, such as tert-butyldimethylsilyl chloride, tert-butyldiphenylsilyl chloride, alkyl halides, such as benzyl chloride or benzyl bromide and sulfonic acid esters such as trifluoromethane-sulfonic acid tert-butyldimethylsilyl ester. Regarding acetal-protecting groups, examples of the reacting agent used for protection are alkoxymethyl halides such as methoxymethyl chloride.
Amount of the reacting agent is equimole or more than equimole to the substrate, preferably 1.0 to 1.2 moles.
Examples of a solvent used are aprotic solvents, such as N,N-dimethylformamide, dimethyl sulfoxide or hexamethylphosphoramide, hydrocarbons, such as benzene or toluene, ethers, such as tetrahydrofuran, 1,4-dioxane, glyme, diglyme or triglyme, or a mixture thereof, when as the base are used alkali metal or alkaline earth metal hydrides, such as sodium hydride or potassium hydride, organic alkali metal salts, such as dimethyl sodium, dimethyl potassium, n-butyllithium, sec-butyllithium or tert-butyllithium, or alkali metal amides, such as lithium diisopropylamide, potassium diisopropylamide, sodium hexamethyldisilazide, potassium hexamethyldisilazide or lithium hexamethyldisilazide.
Examples of a solvent used are aprotic solvents, such as N,N-dimethylformamide, dimethyl sulfoxide or hexamethyl-phosphoramide, hydrocarbons, such as benzene or toluene, ethers, such as tetrahydrofuran, 1,4-dioxane, glyme, diglyme or triglyme, halogen compounds, such as dichloromethane, chloroform or 1,2-dichloroethane, water or a mixture with an organic solvent thereof and water, preferably ethers, aprotic solvents or a mixture of an aprotic solvent and water, especially preferably N,N-dimethylformamide, dimethyl sulfoxide or a mixture of dimethyl sulfoxide and water, when as the base are used alkali metal or alkaline earth metal hydroxides, such as sodium hydroxide or potassium hydroxide, alkali metal or alkaline earth metal hydrogen carbonates, such as sodium hydrogen carbonate or potassium hydrogen carbonate, alkali metal or alkaline earth metal carbonates, such as sodium carbonate or potassium carbonate.
The reaction temperature is from xe2x88x9278xc2x0 C. to reflux temperature of the solvent.
The reaction proceeds without catalyst, but the reaction is promoted in the presence of iodo compounds, such as cesium iodide, potassium iodide or sodium iodide, bromo compounds, such as cesium bromide, potassium bromide or sodium bromide, quaternaryammonium phase transfer catalysts, such as tetrabutylammonium chloride or trimethylbenzyl-ammonium bromide, Crown ethers such as 18-Crown-6, 4-N,N-dimethylaminopyridine, 2,6-lutidine or 4-methoxypyridine, especially effective when a leaving group for the reacting agent used for protection is chlorine atom.
As the reaction promoter, alkali metal bromides or iodides are preferable, especially sodium bromide, potassium bromide, sodium iodide and potassium iodide.
Amount of the reaction promoter is 0.5 to 1.1 moles to compound (7). To use too small amount causes decrease of reaction rate and is not practical.
When R2 is silyl ether-protecting groups, such as triethylsilyl, tert-butyldimethylsilyl or tert-butyldiphenylsilyl, phenyl-substituted methyl-protecting groups, such as benzyl or trityl, or acetal-protecting groups such as methoxymethyl, the protection reaction can be also carried out with halogeno silane compounds, such as trityl chloride or tert-butyldimethylsilyl chloride, alkyl halides, such as benzyl chloride, or benzyl bromide, sulfonic acid esters, such as tert-butyldimethylsilyl trifluoromethanesulfonate, or alkoxymethyl halides such as methoxymethyl chloride in the presence of a tertiary amine, such as triethylamine or pyridine.
Amount of said reagent is equimole or more than equimole to the substrate, preferably 1.0 to 1.2 moles.
Examples of a solvent used are aprotic solvents, such as N,N-dimethylformamide, dimethyl sulfoxide or hexamethyl-phosphoramide, ethers, such as tetrahydrofuran, 1,4-dioxane, glyme, diglyme or triglyme, hydrocarbons, such as benzene or toluene, nitrites such as acetonitrile, halogen compounds, such as dichloromethane, chloroform or 1,2-dichloroethane, or a mixture thereof, preferably aprotic solvents or ethers, especially preferably N,N-dimethylformamide or dimethyl sulfoxide. The reaction is promoted by adding a pyridine derivative, such as 4-N,N-dimethylaminopyridine, 2,6-lutidine or 4-methoxypyridine, preferably 4-N,N-dimethylaminopyridine.
The reaction temperature is from 0C to reflux temperature of the solvent, preferably from room temperature to around 50xc2x0 C.
On the other hand, introduction of tetrahydropyranyl group is carried out by reacting compound (7) and dihydropyrane in the presence of acid catalyst, such as p-toluenesulfonic acid or pyridinium p-toluenesulfonate.
Amount of dihydropyrane is 1 to 1.2 moles to the substrate.
Examples of a solvent are aprotic solvents, such as N,N-dimethylformamide, dimethyl sulfoxide or hexamethyl-phosphoramide, hydrocarbons, such as benzene or toluene, ethers, such as tetrahydrofuran, 1,4-dioxane, glyme, diglyme or triglyme, halogen compounds, such as dichloromethane, chloroform or 1,2-dichloroethane, or a mixture thereof, preferably aprotic solvents or ethers, especially preferably N,N-dimethylformamide or tetrahydro-furan.
The reaction temperature is from xe2x88x9278xc2x0 C. to reflux temperature of the solvent.
Diol compound (5) is prepared by reacting compound (6) with an acid.
Examples of the acid are mineral acids, such as hydrochloric acid or sulfuric acid, organic acid, such as p-toluenesulfonic acid, benzenesulfonic acid, methanesulfonic acid or trifluoroacetic acid, or Lewis acid, such as boron trifluoride etherate, aluminum trichloride, tin tetrachloride or titanium tetrachloride.
Amount of the acid is equimole or more than equimole to the substrate, preferably 1.0 to 1.2 moles.
The solvents, when the acid is a mineral acid or an organic acid, are alcohols, such as methanol, ethanol or 2-propanol, hydrocarbons, such as benzene or toluene, ethers, such as tetrahydrofuran, 1,4-dioxane, glyme, diglyme or triglyme, or a mixture thereof, preferably alcohols, especially methanol. When Lewis acid is used, examples of the solvent are aprotic solvents, such as N,N-dimethylformamide, dimethyl sulfoxide or hexamethyl-phosphoramide, hydrocarbons, such as benzene or toluene, ethers, such as tetrahydrofuran, 1,4-dioxane, glyme, diglyme or triglyme, or a mixture thereof, preferably aprotic solvents or ethers, especially N,N-dimethylformamide or tetrahydrofuran.
The reaction temperature is from 0xc2x0 C. to reflux temperature of the solvent, preferably from room temperature to around 50xc2x0 C.
Compound (3) is prepared by protecting a primary hydroxy group for compound (5) with the protecting group (R1) different from the protecting group (R2) R1 is not limited as long as R1 and R2 can be removed under different condition, and R1 is not removed when R2 is deprotected.
The protecting groups (R1) are different from R2 and are silyl ether-protecting groups, such as triethylsilyl, tert-butyldimethylsilyl or tert-butyldiphenylsilyl, phenyl-substituted methyl-protecting groups, such as benzyl, p-methoxybenzyl or trityl, or acetal-protecting groups, such as tetrahydropyranyl or methoxymethyl.
Each of the protecting groups R1 and R2 is selected from silyl ether-protecting groups, phenyl-substituted methyl-protecting groups and acetal-protecting groups. R1 and R2 are different from each other and are such that only R2 is removed, when the deprotection reaction is carried out.
For example, the following combinations are illustrated; R1 is a silyl ether-protecting group and R2 is a phenyl-substituted methyl-protecting group; R1 is a phenyl-substituted methyl-protecting group and R2 is a silyl ether-protecting group; R1 is a silyl ether-protecting group and R2 is an acetal-protecting group; R1 is an acetal-protecting group and R2 is a silyl ether-protecting group; R1 is a phenyl-substituted methyl-protecting group and R2 is an acetal-protecting group.
More concretely, when R2 is a phenyl-substituted methyl-protecting group, such as benzyl or p-methoxybenzyl, R1 is tetrahydropyranyl, methoxymethyl, trityl, or a silyl ether-protecting group, such as tert-butyldimethylsilyl or tert-butyldiphenylsilyl. When R2 is tert-butyldimethylsilyl, R1 is a phenyl-substituted methyl-protecting group, such as benzyl, p-methoxybenzyl or trityl, an acetal-protecting group, such as tetrahydropyranyl or methoxymethyl, or tert-butyldiphenylsilyl more bulky than tert-butyldimethylsilyl.
When R2 is tert-butyldiphenylsilyl, R1 is a phenyl-substituted methyl-protecting group, such as benzyl, p-methoxybenzyl or trityl, an acetal-protecting group such as, tetrahydropyranyl or methoxymethyl, or dimethylthexylsilyl.
When R2 is an acetal-protecting group, such as tetrahydropyranyl or methoxymethyl, R1 is phenyl-substituted methyl-protecting group, such as benzyl, p-methoxybenzyl except trityl, or a silyl ether-protecting group, such as tert-butyldimethylsilyl or tert-butyldiphenylsilyl. The preferable combination of R1 and R2 is that R2 is tert-butyldimethylsilyl, tert-butyldiphenylsilyl, benzyl or p-methoxybenzyl, and R1 is dimethylthexylsilyl or trityl. The especially preferable combination is one that R2 is benzyl and R1 is trityl.
Introduction of these protecting groups is carried out in accordance with the method of introduction of R2 for compound (7) mentioned above.
Compound (4) is prepared by reacting compound (3) with ethylene glycol derivative (2) after treating compound (3) with a base.
Examples of leaving group (X) of ethylene glycol derivative (2) are halogen, such as chlorine or bromine, sulfonic acid ester, such as methanesulfonyloxy or p-toluenesulfonyloxy, and examples of R2 of ethylene glycol derivative (2) are the same protecting groups as the protective groups (R2) of compound (3) mentioned above, such as benzyl, tert-butyldimethylsilyl, tert-butyldiphenylsilyl, tetrahydropyranyl or methoxymethyl.
Examples of the base used in this reaction are alkali metal or alkaline earth metal hydroxides, such as sodium hydroxide or potassium hydroxide, alkali metal or alkaline earth metal hydrogen carbonates, such as sodium hydrogen carbonate or potassium hydrogen carbonate, alkali metal or alkaline earth metal carbonates, such as sodium carbonate or potassium carbonate, alkali metal or alkaline earth metal hydrides, such as sodium hydride or potassium hydride, organic alkali metal salts, such as dimethyl sodium, n-butyllithium, sec-butyllithium or tert-butyllithium, or alkali metal amides, such as lithium diisopropylamide, potassium diisopropylamide, sodium hexamethyldisilazide, potassium hexamethyldisilazide or lithium hexamethyl-disilazide, preferably alkali metal hydride, alkali metal hydroxide, alkali metal carbonate, especially sodium hydride, sodium hydroxide or potassium hydroxide.
Amount of the base is 1.0-10 moles to the substrate, preferably 1.0 to 2.0 moles.
Examples of a solvent are aprotic solvents such as N,N-dimethylformamide, dimethyl sulfoxide or hexamethyl-phosphoramide, hydrocarbons, such as benzene or toluene, ethers, such as tetrahydrofuran, 1,4-dioxane, glyme, diglyme or triglyme, or a mixture thereof, when as the base are used alkali metal or alkaline earth metal hydrides, such as sodium hydride or potassium hydride, organic alkali metal salts, such as dimethyl sodium, dimethyl potassium, n-butyllithium, sec-butyllithium or tert-butyllithium, or alkali metal amides, such as lithium diisopropylamide, potassium diisopropylamide, sodium hexamethyldisilazide, potassium hexamethyldisilazide or lithium hexamethyl-disilazide.
Examples of a solvent are aprotic solvents such as N,N-dimethylformamide, dimethyl sulfoxide or hexamethyl-phosphoramide, hydrocarbons, such as benzene or toluene, ethers, such as tetrahydrofuran, 1,4-dioxane, glyme, diglyme or triglyme, halogen compounds, such as dichloromethane, chloroform or 1,2-dichloroethane, water or a mixture with an organic solvent thereof and water, preferably ethers, aprotic solvents or a mixture of an aprotic solvent and water, especially preferably N,N-dimethylformamide, dimethyl sulfoxide or a mixture of dimethyl sulfoxide and water, when as the base are used alkali metal or alkaline earth metal hydroxides, such as sodium hydroxide or potassium hydroxide, alkali metal or alkaline earth metal hydrogen carbonates, such as sodium hydrogen carbonate or potassium hydrogen carbonate, alkali metal or alkaline earth metal carbonates, such as sodium carbonate or potassium carbonate.
The reaction proceeds without catalyst, but the reaction is promoted in the presence of iodo compounds such as cesium iodide, potassium iodide or sodium iodide, bromo compounds, such as cesium bromide, potassium bromide or sodium bromide, quaternaryammonium phase transfer catalysts, such as tetrabutylammonium chloride or trimethylbenzyl-ammonium bromide, Crown ethers such as 18-Crown-6, or pyridine derivatives, such as 4-N,N-dimethylaminopyridine, 2,6-rutidine or 4-methoxypyridine, especially effective when the leaving group of a reactive substance used for protection is chlorine atom.
As the reaction promoter, alkali metal bromides or iodides are preferable, especially sodium bromide, potassium bromide, sodium iodide or potassium iodide.
Amount of the reaction promoter is 0.05 to 1.1 moles to compound (3). To use too small amount causes decrease of the reaction rate and is not practical.
The reaction temperature is from xe2x88x92100xc2x0 C. to reflux temperature of the solvent, preferably from 0xc2x0 C. to reflux temperature of the solvent.
The preferable reaction is to react compound (3) with benzyloxyethyl methanesulfonate as ethylene glycol derivative (2), in N,N-dimethylformamide or dimethyl sulfoxide under sodium hydride at 0xc2x0 C. to room temperature or to react compound (3) with benzyloxyethyl methanesulfonate in N,N-dimethylformamide under sodium hydroxide or potassium hydroxide.
Compound (1) is prepared by selectively removing a protective group (R2) of compound (4) When R2 is a phenyl-substituted methyl-protecting group, such as benzyl or p-methoxybenzyl, it is removed under catalytic hydrogenation. Catalysts used in the hydrogenation are heterogeneous catalysts, such as 5% Ptxe2x80x94C, 5%-10% Pdxe2x80x94C, Palladium black or Raney nickel, or homogeneous catalysts such as Wilkinson""s complex.
Amount of the catalyst to a substrate is 1-100% by weight. As hydrogen donor, hydrogen gas, cyclohexene, cyclohexadiene and ammonium formate are illustrated.
Solvents used are alcohols, such as ethanol or 2-propanol, esters, such as methyl acetate or ethyl acetate, ethers, such as tetrahydrofuran, 1,4-dioxane, glyme, diglyme or triglyme, hydrocarbons, such as benzene or toluene, or a mixture thereof, preferably alcohols or esters, especially methanol, ethanol or ethyl acetate.
The reaction is carried out under ambient pressure. The reaction temperature is from 0xc2x0 C. to reflux temperature, preferably from room temperature to reflux temperature.
p-Methoxybenzyl group can be also removed by reacting 2,3-dichloro-5,6-dicyano-1,4-benzoquinone in a solvent, such as ethers, e.g. tetrahydrofuran, 1,4-dioxane, glyme, diglyme or triglyme, or hydrocarbons, such as benzene or toluene.
Preferable deprotection method is subjecting to catalytic reduction with 5% or 10% Pdxe2x80x94C under hydrogen gas in methanol or ethyl acetate under ambient pressure at room temperature.
When R2 is a silyl ether-protecting group such as tert-butyldimethylsilyl, it is deprotected by reacting fluoro anion, such as hydrogen fluoride or tetrabutylammonium fluoride.
Amount of the fluoro anion is 2.0-10 moles to the substrate. Solvents used are ethers, such as tetrahydrofuran, 1,4-dioxane, glyme, diglyme or triglyme, nitriles such as acetonitrile, hydrocarbons, such as benzene or toluene, or a mixture thereof, preferably ethers or nitriles, especially tetrahydrofuran.
The reaction temperature is from 0xc2x0 C. to reflux temperature of the solvent, preferably from room temperature to reflux temperature of the solvent.
The protective group can be removed by reacting a mineral acid, such as hydrochloric acid or sulfuric acid, an organic acid, such as p-toluenesulfonic acid, benzenesulfonic acid, methanesulfonic acid or trifluoroacetic acid, or a Lewis acid, such as boron trifluoride etherate, aluminum trichloride, tin tetrachloride or titanium tetrachloride in an ether, such as tetrahydrofuran, 1,4-dioxane, glyme, diglyme or triglyme, a hydrocarbon, such as benzene or toluene, or a mixture thereof.
The reaction temperature is from 0xc2x0 C. to refluxing temperature of the solvent, preferably 0xc2x0 C. to room temperature. Preferable deprotection method is carried out by reacting 2 moles or more than 2 moles, preferably 2.0-2.2 moles of tetrabutylammonium fluoride to a substrate in tetrahydrofuran at 0xc2x0 C. to room temperature.
When R2 is an acetal-protecting group, such as tetrahydropyranyl or methoxymethyl, it is removed by treating with an acid. The acid used are mineral acids, such as hydrochloric acid or sulfuric acid, organic acids such as p-toluenesulfonic acid, benzenesulfonic acid, methanesulfonic acid or trifluoroacetic acid, or Lewis acids, such as boron trifluoride etherate, aluminum trichloride, tin tetrachloride or titanium tetrachloride.
The acid is used 0.1-10 moles to a substrate, preferably 2-4 moles.
Solvents used are alcohols, such as methanol, ethanol or 2-propanol, ethers, such as tetrahydrofuran, 1,4-dioxane, glyme, diglyme or triglyme, nitriles such as acetonitrile, hydrocarbons, such as benzene or toluene, or a mixture thereof, preferably ethers or alcohols, especially methanol or ethanol.
The reaction temperature is from 0xc2x0 C. to reflux temperature, preferably from 0xc2x0 C. to room temperature.
Preferable deprotection method is carried out by reacting 2 moles of p-toluenesulfonic acid to a substrate in tetrahydrofuran or methanol at 0xc2x0 C. to room temperature.
As shown in the following reaction scheme, after reacting compound (3) with a base, compound (4a) is prepared by reacting compound (2a) or ethylene oxide (2b) therewith, and then, by selectively removing the protecting group (R2) of the compound to give compound (1). 
wherein R1, R2 and X are the same as defined above.
Compound (4a) is prepared by reacting compound (2a) or ethylene oxide (2b) with compound (3), after treating compound (3) with a base.
The reaction of compound (3) with compound (2a) or ethylene oxide (2b) is carried out in the almost same manner as the reaction of compound (3) and compound (2) as mentioned above.
By deprotecting R2 for thus obtained compound (4a) there is obtained butanetriol derivative (1).
The deprotection of R2 can be carried out in the same manner as the method for preparing compound (1) by removing the protecting group (R2) of compound (4) as mentioned above.
Compound (3) is prepared from compound (10) as shown in the following reaction scheme. 
wherein R1 and R2 are the same as defined above, R5 is C1-C6 alkyl, C3-C6 cycloalkyl, phenyl or C1-C6 alkyl substituted phenyl, aralkyl or 2-alkenyl.
Compound (9) is prepared by protecting the primary hydroxy group for compound (10) with the protecting group (R1) different from the protecting group (R2) of compound (3), which is prepared in the latter step.
R1 is not limited as long as R1 and R2 can be removed by the different condition, and R1 is not removed when R2 is deprotected. Examples of R1 and the combination of R1 and R2 are the same described in the above section on the process for preparing compound (3).
Introduction of the protecting group is also carried out in the same manner as introduction of R2 to compound (7).
Compound (8) is prepared by reducing the ester group of compound (9)
Reducing agents are aluminum-reducing agents, such as lithium aluminum hydride or diisobutyl aluminum hydride, or boron-reducing agents, such as sodium borohydride, lithium borohydride, lithium tri-sec-butyl borohydride, potassium tri-sec-butyl borohydride, boron tetrahydrofuran or boron dimethylsulfide complex, preferably lithium aluminum hydride or sodium borohydride.
The reduction is carried out in a solvent such as ethers, e.g. tetrahydrofuran, 1,4-dioxane, glyme, diglyme or triglyme, or hydrocarbons, e.g. benzene, toluene or a mixture thereof. When sodium borohydride is used, an alcohol, such as methanol, ethanol or propanol may be used as a solvent.
Amount of the reducing agent calculated in hydrido ion is 2.0-15 moles to the substrate.
The reaction temperature is from xe2x88x92100xc2x0 C. to reflux temperature of the solvent, preferably xe2x88x9278xc2x0 C. to room temperature.
Compound (3) is prepared by protecting primary hydroxy group for compound (8) with the protecting group (R2) different from R1.
R2 is not limited as long as R1 and R2 can be deprotected by the different condition and R1 is not removed when R2 is deprotected. Examples of R2 and the combination of R1 and R2 are the same described in the above section on processes for preparing compound (6) and compound (3).
Introduction of the protecting group is also carried out in the same manner as introduction of R2 to compound (7).
A compound of the following formula (11) is prepared by bissulfonyl esterification of compound (1) in the presence of a tertiary amine, such as triethylamine or pyridine. 
wherein R6 is C1-C6 alkyl, C3-C6 cycloalkyl, substituted or non-substituted C1-C6 alkyl, halogeno phenyl or nitro phenyl, and R1 is the same as defined above.
By bissulfonyl esterification, crystallizabilty of the product becomes good and therefore, it becomes easy to purify the product by recrystallization.
Sulfonyl halides, such as methanesulfonyl chloride, methanesulfonyl bromide, p-toluenesulfonyl chloride, benzenesulfonyl chloride, or sulfonic acid anhydride such as methanesulfonic acid anhydride are used in the sulfonyl esterification.
Amount of the esterification agent is 2 moles or more than 2 moles to the substrate, preferably 2.0 to 2.2 moles.
Examples of a solvent are aprotic solvents, such as N,N-dimethylformamide, dimethyl sulfoxide or hexamethylphosphoramide, ethers, such as tetrahydrofuran, 1,4-dioxane, glyme, diglyme or triglyme, nitriles such as acetonitrile, halogen compounds, such as dichloromethane, chloroform or 1,2-dichloroethane, or a mixture thereof.
The reaction is promoted by addition of about 0.01 mole of 4-N,N-dimethylaminopyridine.
The reaction temperature is from xe2x88x92100xc2x0 C. to reflux temperature of the solvent, preferably from 0xc2x0 C. to room temperature.
When compounds (7) and (10) are optically active compounds, optically active compound (1) and optically active intermediates (3)-(6), (4a), (8)-(9) and (11) can be obtained. When natural L-malic acid is used as an optically active starting material, (S) formed compound is obtained. When unnatural D-malic acid is used as an optically active starting material, (R) formed compound is obtained.
These compounds are led to compound (10) by two steps and to compound (7) by 3 steps.
It is also possible to use xcex2-hydroxy-xcex3-butyrolactone as an optically active starting material. xcex2-Hydroxy-xcex3-butyrolactone is prepared by the method described in Japanese Patent Publication A 9-47296, and the compound can be led to compound (10) by the method described in Japanese Patent Publication A 4-149151.
Significant racemization does not occur during synthesis of these optically active compounds and therefore, there is obtainable compound (1) with highly optical purity.
Starting compounds (2), (7) and (10) are prepared as follows.
Compound (7) is prepared by acetalization of the adjacent hydroxy groups of 1,2,4-butanetriol in the presence of acid catalyst.
Examples of acetalization agents are ketones, such as acetone, diethyl ketone, benzophenone, cyclohexanone, aldehydes, such as acetoaldehyde or benzaldehyde, dialkoxyacetals of ketone, such as 2,2-dimethoxypropane or 3,3-dimethoxypentane, or enol ethers of ketone such as 2-methoxypropene.
Examples of the acid catalysts are mineral acids, such as hydrochloric acid or sulfuric acid, organic acids, such as p-toluenesulfonic acid, benzenesulfonic acid, methanesulfonic acid or trifluoroacetic acid, or Lewis acids, such as boron trifluoride etherate, aluminum trichloride, tin tetrachloride, or titanium tetrachloride.
Amount of the acid catalyst is 0.05-0.1 mole to the substrate.
Examples of the solvents are aprotic solvents, such as N,N-dimethylformamide, dimethyl sulfoxide or hexamethylphosphoramide, ethers, such as tetrahydrofuran, 1,4-dioxane, glyme, diglyme or triglyme, halogen compounds, such as dichloromethane, chloroform or 1,2-dichloroethane, or acetalization agents themselves, preferably aprotic solvents or acetalization agents themselves, especially preferably N,N-dimethylformamide or acetone.
For example, a compound, wherein R3 and R4 are methyl, is prepared by a method described in the literature (J. Org. Chem., 53, 4495 (1988), that is, by reacting 2,2-dimethoxypropane in the presence of catalytic amount of p-toluenesulfonic acid in N,N-dimethylformamide.
Ethylene glycol derivative (2) is prepared by a method described in the literature (J. Am. Chem. Soc., 60, 1472-1473 (1938). For example, a compound (2), wherein R2 is benzyl, is prepared by reacting 0.25 moles of benzyl bromide or benzyl chloride with 5 moles of ethylene glycol in which 0.25 mole of potassium hydroxide was dissolved. Furthermore, by halogenation of another hydroxy group with thionyl chloride or carbon tetrachloride, or sulfonyl esterification of another hydroxy group with methanesulfonyl chloride or p-toluenesulfonyl chloride, there is obtainable a compound (2), wherein X is a leaving group. A compound, wherein R2 is another protective group, is prepared by using tert-butyldimethylsilyl chloride or methoxymethyl chloride in stead of benzyl halide.
Compound (10) is prepare by reducing malic acid ester, such as methyl ester, ethyl ester, propyl ester, isopropyl ester, butyl ester, cyclohexyl ester, phenyl ester, 4-methylphenyl ester, benzyl ester or allyl ester in a method described in the literature (Chem. Lett., 1984, 1389-1392), namely by selectively reducing one of ester groups with boron dimethylsulfide or sodium borohydride in tetrahydrofuran at room temperature.
On the other hand, compound (10) is prepared by reacting xcex2-hydroxy-xcex3-butyrolactone with alcohol in acidic condition or by subjecting it to ring opening reaction with alkoxide, such as sodium methoxide or sodium ethoxide.
The present invention is explained by following examples, but scope of the invention should not be limited by these examples.